There are more than 8.5 million temporary and contract employees hired by staffing firms every year, according to the American Staffing Association. Nearly eight in 10 (79 percent) work on a full-time basis.

Job assignments range from day laborer to CEO, according to the ASA, with the fastest growth occurring in professional and technical occupations.

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There are about 6,000 staffing firms that have been in business a year or more. Those companies operate approximately 20,000 offices. ASA member companies operate more than 15,000 offices across the nation and account for more than 85% of U.S. industry sales.